The present invention relates to a fused carbonate-type fuel cell, and especially to the structure of a reforming catalyst body thereof.
Conventionally there have been employed internal reforming types of fused carbonate-type fuel cells employing a reforming catalyst as shown in FIG. 3. The fuel cell as used heretofore and as shown in FIG. 3 comprises an electrolyte matrix 1, an electrode 2 on the fuel gas side, an electrode 3 on the oxidizine gas side, both electrodes being adjacent to opposite surfaces of the matrix 1, a partition plate 4a for supporting the fuel gas side electrode 2 and separating a reforming catalyst 7, as hereinafter described in more detail, from the electrode 2, a supporting plate 4b for supporting the other electrode 3, corrugated plates 5a and 5b, forming reaction gas passages on the fuel gas side and on the oxidizing gas side, respectively, and a separator plate 6. The separator plate 6 acts to separate a fuel gas passage from an oxidizing gas passage and also acts to electrically connect in series a plurality of single cells comprising the electrolyte matrix 1, the electrode 2 on the fuel gas side, and the electrode 3 on the oxidizing gas side when a number of single cells are stacked one another. The reforming catalysts 7, disposed on both sides of the corrugated plate 5a on the fuel gas side, comprises nickel supported on a alumina-magnesia based carrier. These catalysts are commercially available in a spherical or cylindrical form, and are generally several mm in size.
The operation of the above-mentioned cell will now be described. A fuel gas comprising a hydrocarbon and steam as the major components and an oxidizing gas comprising oxygen and carbon dioxide as the major components are fed to the fused carbonate-type fuel cell in a cross flow into the fuel gas passage and the oxidizing gas passage, respectively. The hydrocarbon component in the fuel gas is converted upon contact with the reforming catalyst 7 in the presence of steam to a fuel gas comprising hydrogen and carbon monoxide as the main component as shown in Equations (1)-(3) set forth below: ##STR1## These reactions are as a whole endothermic and therefore are carried out by utilizing heat produced in the fused carbonate-type fuel cell. The resultant gases containing hydrogen and carbon monoxide diffuse through holes in the partition plate 4a and oxygen and carbon dioxide in the oxidizing gas diffuse through holes in the supporting plate 4b. Thus, the hydrogen and carbon monoxide and the oxygen and carbon dioxide react on the electrode 2 on the fuel gas side and on the electrode 3 on the oxidizing gas side as follows:
On the electrode 2 on the fuel gas side, EQU H.sub.2 +CO.sub.3.sup.2- .fwdarw.H.sub.2 O+CO.sub.2 +2e (4) EQU CO+H.sub.2 O.fwdarw.H.sub.2 +CO.sub.2 ( 5)
On the electrode 3 on the oxidizing gas side, EQU 1/2O.sub.2 +CO.sub.2 +2e.fwdarw.CO.sub.3.sup.2- ( 6)
By these chemical-electrochemical reactions the chemical energy contained in the fuel gas is converted to electrical energy and thermal energy. Most of the thermal energy thus produced is utilized as set forth before to supply the heat required for the reaction heat in order to decompose the hydrocarbons in the gas flow passage by contact with the catalyst 7. This means a significant improvement in heat efficiency, which is one characteristic of the internal reforming system.
In the above system, however, since the commercially available reforming catalysts 7 are in the form of spherical or cylindrical particles it is necessary to hold the particles of the reforming catalyst 7 in the fuel gas passages by packing them as shown in FIG. 3. However, such packing and holding of the catalyst makes its handling very difficult during fabrication of the internally reforming-type fused carbonate salt fuel cell. Also uniform packing of the catalyst is achieved only with difficulty which makes it difficult to achieve uniform contact for the reactant gas with the reforming catalyst 7, with the results that no effective utilization of the reforming catalyst 7 takes place.
Further, the reforming catalyst 7 decreases in activity on contact with an electrolyte contained in the electrode 2 on the fuel gas side or in the electrolyte matrix 1. In order to avoid such a decrease in activity, the catalyst particles must be prevented from making direct contact with the electrolyte by the partition plate 4a. However, the contact of the reforming catalyst 7 and the electrolyte may happen due to vibration or upon supplying the electrolyte. If such contact should occur wetting of only a portion of the catalyst with the electrolyte may spread over a wide area of the catalyst because of the construction being such that the catalyst particles are held in contact with each other, with the results that significant reduction of the activity of the catalyst will take place.
As the fused carbonate-type fuel cells employing the reforming catalyst of the prior art have the constitution as set forth above, they have the drawbacks that resistance to wetting is low, uniform contact between the reforming catalyst and the reaction gases is difficult, and handling upon fabrication of the cells is cumbersome.